Troops look cross mounting guard at entrance (10)
I believe the answer is:
doorkeeper
'guard at entrance' is the definition.
(guard by a door)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for doorkeeper that I've seen before include "He attends an opening" , "Admission controller" , "Person on duty at entrance" , "Porter" , "One on duty at building's entrance" .)